1. Field of the Invention
The present invention is directed to a rolled paper feeding apparatus used in an image forming apparatus such as a facsimile machine, printer, digital copier, and the like. More particularly, the present invention is directed to an apparatus for providing resistance against the feeding out of paper in order to uncurl the rolled paper. The present invention is further directed towards a torque limiting device for providing a constant angular force (torque) which is used for unrolling the paper.
2. Discussion of the Background
FIG. 1A illustrates a conventional facsimile device 100 which utilizes rolled paper 1. The rolled paper 1 which will have an image recorded thereon is set into a receiving bin in the direction of arrow `A`. In the device 100, the paper is not supported in any manner at the rotational axis but rests on the bottom of the paper bin. Therefore, there is no need to use any type of paper spool or collar with the paper 1 in the facsimile machine 100.
FIG. 1B illustrates a different type of rolled paper facsimile machine which utilizes a paper spool 2 or support device made up of a shaft 2a and a side plate 2b. The rolled paper 1 with the spool is used to allow the paper to be smoothly pulled off of the roll as the roll of paper 1 is rotating. The support 2 may be referred to as a spool, spindle, spur, or other device which supports the rolled paper 1 as the roll is rotating. In FIG. 1B, the supports 2 are pushed against the roll of paper in the direction of the arrows `B` and the rolled paper 1 having the two supports 2 is inserted into the facsimile machine 102 in the direction of arrow `C`. In FIG. 1B, the shaft 2a may freely rotate with respect to the side plate 2b, or alternatively, the shaft 2amay be fixed to the side plate 2b and therefore, the side plate 2b will rotate inside of the facsimile machine 102.
FIG. 2 is a cross-sectional view of the roll of paper 1 which includes a plurality of layers of paper 1a and a cardboard core 1b. In FIG. 2, a collar 3 is tightly inserted into the cardboard core 1b and the shaft 2a of the support device is inserted into the collar 3. The collar 3 is fixed with respect to the cardboard core 1b of the rolled paper 1 whereas the collar 3 and roll of paper 1 rotate freely with respect to the shaft 2a and the support 2.
FIG. 3 illustrates a conventional manner of uncurling the paper from the roll of paper 1. A pair of transport rollers 112 and 114 pull the paper around a decurling roller 110 so as to correct a curling of the paper in an opposite direction to a paper winding direction on the roll with a force of Fa. The rolled paper 1 provide a resistance against the force Fa in order to uncurl the paper around the decurling roller 110.
However, the decurling system illustrated in FIG. 3 has a drawback in that as the roll of paper uncurls, the paper must be under a higher tension around the decurling roller 110 to properly decurl the paper as the radius of the rolled paper 1 gets smaller. This is because the paper wound at a smaller radius (e.g., at a region closer to the core of the rolled paper) requires more tension to properly decurl the paper because the curl of the paper is smaller or tighter near the core. The frictional force imposed against the turning of the rolled paper 1 is partially dependent on the weight of the paper. As the weight of the rolled paper 1 becomes lighter, less force against the pulling of the paper in the direction Fa is imparted. Therefore, even as the radius of the rolled paper decreases which results in an increase in the force which prevents the unrolling operation, unsatisfactory force used for decurling may result due to the decrease in weight of the paper.
FIG. 4 illustrates three different relationships designated by the lines `A`, `B` and `C`. `A` is the ideal curve which would achieve the optimum paper decurling. The curve `A` shows an inverse linear relationship between the force Fa (in Newtons, for example) and the radius of the rolled paper (in centimeters). The line `B` shows a first example of the force Fa of a conventional system. For example, the line `B` can illustrate a roll of paper having a relatively small diameter core which is smooth. Also for example, the curve `C` illustrates the force for a small diameter core of a roll of paper which is somewhat dented. It can be seen in FIG. 4 that the slope of the ideal line `A` has the force increasing as the radius of the rolled paper decreases whereas neither lines `B` nor `C` have an increase in force as the radius of the rolled paper decreases.